The skeletal system includes many long bones that extend from the human torso. These long bones include the femur, fibula, tibia, humerus, radius and ulna. These long bones are particularly exposed to trauma from accidents and as such often are fractured during such trauma and may be subject to complex devastating fractures.
Automobile accidents, for instance, are a common cause of trauma to long bones. In particular, the femur and the tibia frequently fracture when the area around the knee is subjected to frontal automobile accidents.
Often the distal or proximal portions of a long bone, for example, the femur and the tibia are fractured and must be reattached.
Mechanical devices, most commonly in the form of pins, plates, and screws are commonly used to attach fractured long bones. The plates, pins and screws are typically made of a durable material compatible with the human anatomy, for example a metal such as a titanium alloy, a stainless steel alloy, or a cobalt chromium alloy. The plates are typically positioned longitudinally along the periphery of the long bone and have holes or openings through which screws may be inserted into the long bones transversely. Additionally, intramedullary nails or screws may be utilized to secure fractured components of a long bone, for example, the head of a femur.
There are a variety of other devices used to treat femoral fractures. Fractures of the neck, head or intertrochantor of the femur have been successfully treated with a variety of compression screw assemblies, which include, generally, a compression plate having a barreled member, a leg screw, and a compressing screw. The compression plate is secured to the exterior of the femur and the barreled member is inserted into a predrilled hole in the direction of the femoral head. The leg screw, which has a threaded end and a smooth portion, is inserted through the barrel member so that it extends across the break and into the femoral head. The threaded portion engages the femoral head. The compression screw connects the leg screw to the plate. By adjusting the tension of the compressions screw the compression of the fracture can be adjusted. The smooth portion of the leg screw must be free to slide through the barrel member to permit the adjustment of the compression screw.
Subtrochantric and femoral head fractures have been treated with the help of intramedullary rods, which are inserted into the marrow canal of the femur to immobilize the femur parts involved in the fracture. A single angle cross nail or locking screw is inserted through the femur and the proximal end of the intramedullary rod. In some varieties, one or two screws may be inserted through he femoral shaft and through the distal end of the intramedullary rod. The standard intramedullary rods have been successfully employed in treating fractures in lower portions of the femoral shaft.
Intramedullary rods or nails are used by orthopaedic surgeons to treat fractures involving long bones such as the femur, humerus, tibia, fibula, etc. The medullary canal of the fractured bone is drilled out or otherwise opened from one end and the intramedullary nail and is longitudinally placed within the medullary canal to contact at least two fragments, i.e., such that the nail extends on both sides of the fracture. As used herein, the term fragment, refers to a portion of a fractured bone regardless of whether the fracture is complete. When implanted, the nail strengthens and supports fragments of the fractured bone during healing of the fracture.
Various types of intramedullary rods or nails are well known within the medical device arts, and several different methods have used to attach the intramedullary nail within the bone. For instance, in U.S. Pat. No. 4,338,926 to Kummer, et al, an intramedullary nail is disclosed which places a compressive force regularly outside of the interior wall of the cortex structure surrounding the intramedullary nail. The compressive force secures the Kummer nail within the medullary canal of the fragments.
Similarly, in U.S. Pat. No. 4,457,301 to Walker a flexible plastic core element holds longitudinal pins of intramedullary nail in place. In U.S. Pat. No. 5,514,137 to Coutts, cement is injected through a cannula in an intramedullary nail to secure the distal end of the intramedullary nail to a bone. The medullary nail designs may employ a more secure and mechanically positive attachment to the bone, such as through use of one or more fasteners, which extend transversally to the longitudinal axis of the nail and through the cortex of the bone.
The bone fastener is received within a receiving recess or through the hole within the intramedullary nail to secure the intramedullary nail relative to the bone fastener. In the transverse attachment, the receiving opening defines an axis, which is at an angle to the longitudinal axis of the nail; 90 degrees and 45 degrees are common. The bone fastener is attached onto this receiving opening axis.
U.S. Pat. No. 4,733,654 to Morino, U.S. Pat. No. 5,057,110 to Krantz, et al, U.S. Pat. No. 5,127,913 to Thomas, Jr., U.S. Pat. No. 5,514,137 to Coutts and others disclose such a transverse bone fastener attachment in a bicordical attachment. U.S. Pat. No. 5,454,438 to Penning, shows a nail design with a recess, which permits only unicordical attachment. The present invention relates particularly to intramedullary nails, which use bone fasteners through the cortex for attachment.
Intramedullary nails are secured in the medullary canal by use of the fasteners to connect the nail to the cortical bone of the long bone. The attachment of the nail to the bone may be accomplished by one of two alternate methods. The first method is static locking in which the nail is rigidly secured to the screw and to the cortical bone. Such static locking provides for a secure attachment of the nail to the bone and promotes initial healing of the fracture site.
Due to a phenomenon often referred to as Wolff's law, the healing over time of bone around a fracture site is promoted if the fracture site is under load or stress. This phenomenon known as Wolff's law is due to the fact that if the bone at the fracture site is not under load, the bone tends to atrophy. The use of the static locking method therefore reduces the load at the fracture site and may subject the fracture site to atrophy. For such reasons, an alternate locking method may be desired.
Such an alternate locking method is known as a dynamic locking. Under dynamic locking, the fastener is movably secured to the opening of the intramedullary nail. Such movement may be accomplished by permitting the fastener to move along the axis of the opening or by providing an elongated opening in which the fastener may move with respect to the IM nail.
More recently, medullary nails have been designed which include a resorbable material positioned in the openings in which the fasteners are inserted for securing the nail through the bone. In such configuration, the intramedullary nail at the time of surgery operates in the static locking method and as the fracture site begins to heal, the body resorbs the resorbable material and the fastener is permitted to move with respect to the intramedullary nail. Such a nail with a resorbable insert is shown in U.S. Pat. No. 6,296,645 to Hover, et al, hereby incorporated by reference in its entireties.
To provide for an option for the surgeon to provide for static and dynamic locking for the same intramedullary nail, intramedullary nails have been designed with slots elongated in the longitudinal direction of the intramedullary nail. With such intramedullary nail slots, the nail may be used in a dynamic mode by placing the screw centrally in the slot or may be used in a static mode by positioning the fastener at the distal end of the slot. When used in a static mode, the nail can only be positioned in static mode in one position. The condition of the bone may be such that the position available for static locking may not be possible due to damage to the bone at that position.
The present invention is designed to overcome at least one of the aforementioned problems.